Variable inductance coupling loop



June 4, 1957 c. R. ELLIS VARIABLE INDUCTANCE COUPLING LOOP Filed Feb.27, 1956 FIG.I

IIIIIIIIAEVIIIA "IQVENTOR: CHARLES R. ELLIS,

HIS AGENT.

United States Patentjf) "ice 2,794,960 VARIABLE INDUCTANCE COUPLING LOOPCharles R. Ellis, North Syracuse, N. Y., assignor to General ElectricCompany, a corporation of New York Application February 27, 1956, SerialNo. 568,067 7 Claims. .(Cl. 333-24) This invention relates to the art ofelectromagnetic coupling arrangements and more particularly to the artvcaused the development of cavity-resonator type oscilla tors andamplifiers. A problem associated with the. development of these types ofequipments .has been the problem of coupling electromagnetic energywithin such oscillators to conductive cabling for transmission toequipments utilizing this electromagnetic energy. One type of apparatusdeveloped by the prior art for such coupling arrangements has been thatof a coupling loop inserted into the electromagnetic field within thegenerator. The variation of magnetic fields within the generator willinduce a corresponding electrical signal in said loop for transmissionto a transmission line such as coaxial cable. It has always beendesirable to'arrange the coupling loop in such manner as to enableadjustment of'the effective area of the loop within the electromagneticfield. In this manner, the delivered power can be varied. The need foradjustment of the loop area within the oscillator while maintaining anelectrical seal has involved adjustable devices having many slidingjoints which exhibit difficulty in maintenance and operation.

It is an object of my invention to provide a variable inductancecoupling loop obviating this difficulty.

It is a further object of my invention to provide the coupling loophaving an inductance variableby external adjustment which is both simpleand efficient inoperation.

It is a further object of my invention to provide a variable inductancecoupling loop having but one sliding joint.

It is a further object of my invention to provide animproved means inand relating to signal coupling arrangements.

In accordance with these objects, I have provided, in one embodiment ofmy invention, a coupling loop attached immovably to :the centerconductor of :a coaxial cable and inserted within a cavity resonatorthrough a cylindrical tube or sleeve. By movementof 'thecylindricalsleeve along the length of the loop, the efiective loop 1 'area insertedwithin the cavity resonator .is changed and therefore the poweroutput-derived from the cavity resonator can be varied.

In a modification of my invention, I have provided in one embodiment, amulti-turn spiral integrally formed with the loop and surrounding thesleeve in the resonator. At the operating frequency, a change .in theposition of the sleeve will give a greater percentage change/ofeffective coupling than a straight-legged loop.

The features of my invention which I believe to be novel, are set forthwith particularity in the appended claims. My invention itself, however,.both astoits a0]?- ganization and method of operation, togetherwithfurther objects and advantages thereof, may best be .understood byreference to the following descriptiontaken in, t

I existing within the cavity resonator.

2,794,950 Patented June 4, 1957 connection with the accompanyingdrawings in which: Figure .1 is a cross-sectioned plan view of astraightlegged coupling loop according to the present invention;

and

Figure 2 is a cross-sectional plan view of a spiral type coupling loopin accordance with the present invention.

Referring now to Figure 1, there is shown a loop inserted within asource of varying electromagnetic energy such as the cavity of a cavityresonator, the walls of which are shown as 1. A shorting plate 2electrically con- .tacts the cavity walls by means of spring contacts 3.The spring contacts permit movement of theplate without changing theelectrical contact. .In this manner, the shorting plate 2 can be movedand positioned within the cavity resonator to determine the operatingresonant frequency of the. cavity resonator in a well known manner. Thecoupling element or loop comprises a shorter leg and a longer legintegrally formed with and connected by a U- shaped member 4. The loopis inserted through the shorting plate. T he longer leg makes contactwith the center conductor 5 of the coaxial line 6 which is rigidlyfastened to a support such as a frame member. A sleeve 7 surrounds thelonger leg of. the loop making contact with the outer conductor of thecoaxial line 6 at its lower ex- 25v tremity. The cylinder is maintainedat the .same potential as the shorting plate by wiping contacts. 8affixed over the bearing 9 which maintains the axial alignment of sleeve7. The sleeve 7 is movable over the lengthof the coupling loop, and isdriven by the coupling loop motor 10 acting through the spur gear 1'1and rack 12. Since the coaxial line is fixed, contact with the outerconductor 6 is maintained by a sliding contact along the surface 13.Shortingfingers or contacts 14 may be provided at the top of sleeve 7contacting the shorter leg of the coupling loop. The shorting contacts14 may be .mounted on a conductive block 15 afiixed to the sleeve 7. Aninsulating block 16 is provided in the tube to maintain concentricity oraxial alignment of the longer leg with the sleeve 7. The material usedfor the conductive components is preferably silver-plated brass.

In operation, after the shorting plate has'been adjusted for the properresonant frequency of the cavity resonator, the sleeve 7 can be removedby operation of the coupling loop motor 10 to travel up and down inorder to properly adjust' the effective area of loop 4 projected withinthe resonator cavity. Since the sleeve travels as a unit, it is possibleto place tuning impedance sections within the lower half of thesleeve'which are effective throughout the range of sleeve travel sincethe sleeve length to the tuning section is not varied.

As the sleeve is moved with respect to the loop, the conductive surfaceof the loop will shield the portion of the loop 4 contained within thetube from the magnetic fields Therefore, movement of the tube will varythe effective area of the loop exposed to these, magnetic fields and vary the power coupled into the coaxial cable.

The variation in effective areaproduced by movement of the tube 7 occurswith or without the shorting contacts 14. However, in many cases it ispreferable to employ the shorting contacts 14 because of the greaterefiective percentage change of exposed loop area with a fixed change inmotion of the coaxial sleeve. At low frequencies the variable inductancecoupling loop shown in Figure lrnay become somewhat cumbersome and themodification shown in Figure 2 may preferably be employed.

In Figure .2 is shown a form of coupling loop suitable for low frequencyoperation. A loop' such as this was satisfactorily operated at afrequency of approximately .megacyclesper second and lower. In thisfigure,

,partsj similar to those shown in Figure 1 are identically t a numbered.As in Figure 1, a sleeve 7 passes through the shorting plate 2. Thecoupling loop has a member which is concentric with the walls of saidsleeve and contacts the internal connector of the coaxial cable 6. The

sleeve slidingly contacts the external conductor of the coaxial cablealong surface 13. r The coupling loop is formed in' a manner similar tothat of Figure 1, but with the member inside the oscillator formed in ahelix extending around the outside wall of the tube 7.

The end of the helix is secured to the shorting plate by a screw 24 orother appropriate method. The convolutions of the helix pass through ahole in a tab 25 securely affixed to the wall of sleeve 7.= Rotation ofthe sleeve a helix allows much greater change in the loop coupling.-

for a given linear movement of the concentric tube 7. At lowfrequencies, this is particularly important, by greatly decreasing therelative sleeve movement which would be necessary with a coupling of theform shown in Figure 1 for the same change in coupling. Contacts similarto contacts 14, Figure 1, may be employed if the electrical contactprovided by tab 25 is not sufficient.

While. particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from theinvention in the broader aspects: and, therefore, the aim in theappended claims is to cover all such changes andmodifications as fallwithin the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l.In combination, in a cavity resonator having a resonant frequencyadjusting plate with an aperture therein, a cylindrical sleeve extendingthrough said aperture, a bearing, said bearing mounted in said apertureand adapted to support said sleeve by slideable contact there with, afirst contact means mounted on said plate and slideably contacting saidsleeve, a coupling element within said resonator, said element having alonger and shorter leg integrally formed with and joined by a U-shapedsection, said element having said longer leg positioned within saidsleeve and said shorter leg positioned outside of said sleeve, means foraxially aligning said longer leg within said sleeve by sliding contacttherewith, means for mounting said shorter leg to said shorting plate, asecond contact means mounted within said resonator near the end of saidsleeve and slideablycontacting said shorter leg, a coaxial cable havinga center and outer conductor, means coupling said longer leg to saidcenter conductor, said outer conductor being surrounded by and inslideable contact with said sleeve outside of said resonator, means formoving said sleeve along said longer leg of said coupling element.

2. In combination, in a cavity resonator having a resonant frequencyadjusting plate with an aperture therein, a cylindrical sleeve extendingthrough said aperture, a bearing mounted in said aperture and adapted tosupport said sleeve by slideable contact therewith, a first contactmeanslmounted on said plate and in slideable contact with said sleeve, acoupling element within said resonator, said element having a first andsecond leg integrally formed with and joined by a U-shaped section, saidelement having said first leg positioned within said sleeve and saidsecond leg positioned outside of said sleeve, means for axially aligningsaid first leg Within said sleeve by sliding contact therewith, acoaxial cable having a center and outer conductor, means coupling saidfirst leg to said cen- A. ter conductor, said outer conductor beingsurrounded by and in slideable contact with the sleeve outside of saidresonator, said second leg being formed in a helix surrounding saidsleeve, securing means adapted to secure said helix to said frequencyadjusting plate, tab means affixed to said sleeve within said resonatorand mechanically coupled to said helix in a manner to cause the sleeveto ride the helix when sleeve is rotated, and means for rotating saidsleeve.

3. In combination, in a source of varying electromagnetic fields havinga frequency adjusting plate with an aperture therein, a sleeve ofelectrically conducting material extending through said aperture and inelectrical contact with said plate, a coupling element, said elementhaving a first and second leg integrally formed with and joined by aU-shaped section, said U-shaped section positioned within said source,said first leg positioned Within said sleeve and extending through saidplate, means for axially aligning said first leg within said sleeve bysliding contacting therewith, means for securing said second leg to saidplate, means for electrically connecting said second leg with the end ofsaid sleeve within said source by sliding contact therewith, a coaxialcable having a center and outer conductor, means connecting said firstleg to said center conductor, said outer conductor being surrounded byand in slidable contact with said sleeve outside of said source, meansfor moving said 'sleeve along said first leg.

4. In combination, in a source of varying electromagnetic fields havinga frequency adjusting plate with an aperture therein, a sleeve ofelectrically conducting material extending through. said aperture and inelectrical contact with said plate, a coupling element, said elementhaving a first and second leg integrally formed with and joined by aU-shaped section, said U-shaped section positioned within said source,said first leg positioned within said sleeve and extending through saidplate, means for axially aligning said first leg Within said sleeve bysliding contact therewith, means for securing said second leg to saidplate, means for electrically connecting said second leg with the end ofsaid sleeve within said source by sliding contact therewith, a coaxialcable having a center and outer conductor, means connecting said firstleg to said center conductor, said outer conductor being surrounded byand in slideable contact with said sleeve outside of said source, meansfor moving said sleeve to vary the sleeve length within said source.

5. In combination a cavity resonator, a shorting plate associated withsaid resonator for changing the effective volume of said resonator, aconductive sleeve adjustably protruding through an opening in said plateinto said resonator, a cable having an inner and an outer conductor, acoupling loop positioned within said cavity resonator and having one endphysically connected to said plate and the remaining end connectedthrough said sleeve to the inner conductor of said cable, and said outerconductor slideably connected to the portion of said sleeve protrudingoutside said cavity resonator.

6. In combination, in a source of varying electromagnetic fields havingan enclosing wall with an aperture therein, a sleeve of electricallyconducting material extending through said aperture and in electricalcontact. with said Wall, a coupling element, said element having a firstand second leg integrally formed with and joined by a U-shaped section,said U-shaped section positioned within said source, said first legpositioned within said sleeve and extending through said plate, meansfor axially aligning said first leg within said sleeve by sliding con-'ing contact therewith, a coaxial cable having a center and outerconductor, means connecting said first leg to said center conductor,said outer conductor being surrounded by and in slideable contact withsaid sleeve out- 5 side of said source, means for moving said sleeve tovary the sleeve length within said source.

7. In combination, in a source of varying electromagnetic fields havingan enclosing wall with an aperture therein, a cylindrical sleeveextending through said aperture, a bearing mounted in said aperture andadapted to support said sleeve by slidable contact therewith, a firstcontact means mounted on said plate and in slideable contact with saidsleeve, a coupling element within said source, said element having afirst and second leg integrally formed with and joined by a U-shapedsection, said element having said first leg positioned within saidsleeve and said second leg positioned outside of said sleeve, means foraxially aligning said first leg within said sleeve by sliding contacttherewith, a coaxial cable having a 15 center and outer conductor, meanscoupling said first leg to said center conductor, said outer conductorbeing surrounded by and in slideable contact with the sleeve outside ofsaid resonator, said second leg being formed in a helix surrounding saidsleeve, securing means adapted to secure said helix to said enclosingWall, tab means affixed to said sleeve within said resonator andmechanically coupled to said helix in a manner to cause the sleeve toride the helix when sleeve is rotated, and means for rotating saidsleeve.

Van Beuren June 28, 1949 Sydoriak Jan. 12, 1954

